Field of the Invention
The present invention relates to a technical improvement of a working machine in which a belt-type continuously variable transmission is interposed in a working power transmission system from a drive source to a working unit.
Description of the Related Art
A belt-type continuously variable transmission for a working machine is a transmission capable of continuously changing a speed reduction ratio of a driven pulley to a drive pulley. In order to enhance the working efficiency of a working machine and the degree of freedom of work, it is preferable that a worker can optionally regulate the working speed of the working unit, and the traveling speed of the traveling unit.
As a working machine like this, an auger snowplow is cited, for example. A general auger snowplow can scrape up snow by the auger at a front part while traveling forward by a power source, and blow the snow which is scraped up to a distance via a chute by a blower. A load that is applied to the auger and the blower, that is, the load on the snow removal working unit successively changes due to various factors such as the density of snow, a snow removal height, and a snow throwing distance. In this relation, the art in which a belt-type continuously variable transmission is interposed in a working power transmission system from a drive source to a snow removal working unit is known from Japanese Utility Model Laid-Open No. 05-040096.
The belt-type continuously variable transmission known in Japanese Utility Model Laid-Open No. 05-040096 is composed of a drive pulley that is provided at an output shaft of an engine, a driven pulley that is provided at a drive shaft of an auger and a blower, a V-belt that is laid between the drive pulley and the driven pulley, and a tension pulley that is located in the middle of the V-belt. The driven pulley is composed of a fixed sheave provided at the drive shaft, a movable sheave displaceable in an axial direction with respect to the fixed sheave, and a spring that urges the movable sheave to the fixed sheave. The tension pulley is driven by a hydraulic cylinder to advance and retreat with respect to the V-belt.
A worker optionally operates an operation unit in accordance with the quality of snow to be removed. A control device extends and contracts the piston of the hydraulic cylinder by performing drive control of a hydraulic pump in accordance with the operation signal of the operation unit. When the piston extends, and thereby the tension pulley presses the V-belt, the tension of the V-belt increases. In accordance with increase in tension, the movable sheave alienates in the axially longitudinal direction with respect to the fixed sheave. When the piston contracts, and thereby the pressing force to the V-belt by the tension pulley reduces, the tension of the V-belt decreases. In accordance with decrease in the tension, the movable sheave moves closer to the fixed sheave. In this manner, in accordance with the displacement amount of the movable sheave to the fixed sheave, an effective diameter of the driven pulley changes. As a result, the speed reduction ratio of the driven pulley to the drive pulley can be continuously changed.
The driven pulley of an ordinary belt-type continuously variable transmission is provided with a well-known torque cam mechanism. The torque cam mechanism converts a part of torque that is transmitted to the movable sheave from the V-belt into thrust, and is known from Japanese Patent Laid-Open No. 05-060192, for example. It is preferable to also provide the torque cam mechanism in the belt-type continuously variable transmission which is known by Japanese Utility Model Laid-Open No. 05-040096. A belt-type continuously variable transmission can smoothly perform a displacement operation of the movable sheave by including the torque cam mechanism.
However, in a densely built-up residential area, a careful operation is required so that thrown snow does not enter the grounds of adjacent houses. The worker frequently needs to adjust the snow throwing direction and the snow throwing angle of the chute, and the operation is troublesome. In this way, in order to enhance the snow removing workability of the auger type snowplow, there is yet room for further improvement. The same also applies to various working machines.
Further, when the load of the working unit abruptly increases in this way, the speed reduction ratio temporarily increases (is in a low speed range). That is, the actual working rotational speed of the working unit temporarily becomes low. As a result, a burden of the drive source can be reduced. Meanwhile, when the load on the working unit is abruptly decreased, the speed reduction ratio temporarily decreases (is in a high speed range). That is, the actual working rotational speed of the working unit temporarily becomes high.
When the speed reduction ratio is small, the drive force which is transmitted to the movable sheave from the drive source by the belt is small. If the load is abruptly increased, when the speed reduction ratio is in a small state, the load which acts on the driven shaft at which the fixed sheave is provided can exceed the drive force which is transmitted to the movable sheave from the drive source. In order to perform slide displacement of the movable sheave by the torque cam mechanism smoothly even in the case like this, there is yet room for improvement. In order to perform work by the working unit more smoothly when the drive source is configured by an engine, for example, it is more preferable that occurrence of an engine stall can be prevented.
The present invention has an object to provide an art that can optionally regulate a working rotational speed of a working unit, and can perform stable work by the working unit, in a working machine including a belt-type continuously variable transmission.